From: "Michael S. Tsirkin" <mst@redhat.com>
To: Sasha Levin <sashal@kernel.org>
Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org,
virtualization@lists.linux-foundation.org
Subject: Re: [PATCH AUTOSEL 5.4 28/28] virtio: fix up virtio_disable_cb
Date: Sun, 11 Jul 2021 00:24:47 -0400 [thread overview]
Message-ID: <20210711002423-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20210710235107.3221840-28-sashal@kernel.org>
On Sat, Jul 10, 2021 at 07:51:07PM -0400, Sasha Levin wrote:
> From: "Michael S. Tsirkin" <mst@redhat.com>
>
> [ Upstream commit 8d622d21d24803408b256d96463eac4574dcf067 ]
>
> virtio_disable_cb is currently a nop for split ring with event index.
> This is because it used to be always called from a callback when we know
> device won't trigger more events until we update the index. However,
> now that we run with interrupts enabled a lot we also poll without a
> callback so that is different: disabling callbacks will help reduce the
> number of spurious interrupts.
> Further, if using event index with a packed ring, and if being called
> from a callback, we actually do disable interrupts which is unnecessary.
>
> Fix both issues by tracking whenever we get a callback. If that is
> the case disabling interrupts with event index can be a nop.
> If not the case disable interrupts. Note: with a split ring
> there's no explicit "no interrupts" value. For now we write
> a fixed value so our chance of triggering an interupt
> is 1/ring size. It's probably better to write something
> related to the last used index there to reduce the chance
> even further. For now I'm keeping it simple.
>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
I don't think we should have it in stable just yet.
Let's make sure it fixes the issue first.
> ---
> drivers/virtio/virtio_ring.c | 26 +++++++++++++++++++++++++-
> 1 file changed, 25 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 97e8a195e18f..b6e1e0598529 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -113,6 +113,9 @@ struct vring_virtqueue {
> /* Last used index we've seen. */
> u16 last_used_idx;
>
> + /* Hint for event idx: already triggered no need to disable. */
> + bool event_triggered;
> +
> union {
> /* Available for split ring */
> struct {
> @@ -739,7 +742,10 @@ static void virtqueue_disable_cb_split(struct virtqueue *_vq)
>
> if (!(vq->split.avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) {
> vq->split.avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;
> - if (!vq->event)
> + if (vq->event)
> + /* TODO: this is a hack. Figure out a cleaner value to write. */
> + vring_used_event(&vq->split.vring) = 0x0;
> + else
> vq->split.vring.avail->flags =
> cpu_to_virtio16(_vq->vdev,
> vq->split.avail_flags_shadow);
> @@ -1605,6 +1611,7 @@ static struct virtqueue *vring_create_virtqueue_packed(
> vq->weak_barriers = weak_barriers;
> vq->broken = false;
> vq->last_used_idx = 0;
> + vq->event_triggered = false;
> vq->num_added = 0;
> vq->packed_ring = true;
> vq->use_dma_api = vring_use_dma_api(vdev);
> @@ -1919,6 +1926,12 @@ void virtqueue_disable_cb(struct virtqueue *_vq)
> {
> struct vring_virtqueue *vq = to_vvq(_vq);
>
> + /* If device triggered an event already it won't trigger one again:
> + * no need to disable.
> + */
> + if (vq->event_triggered)
> + return;
> +
> if (vq->packed_ring)
> virtqueue_disable_cb_packed(_vq);
> else
> @@ -1942,6 +1955,9 @@ unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq)
> {
> struct vring_virtqueue *vq = to_vvq(_vq);
>
> + if (vq->event_triggered)
> + vq->event_triggered = false;
> +
> return vq->packed_ring ? virtqueue_enable_cb_prepare_packed(_vq) :
> virtqueue_enable_cb_prepare_split(_vq);
> }
> @@ -2005,6 +2021,9 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
> {
> struct vring_virtqueue *vq = to_vvq(_vq);
>
> + if (vq->event_triggered)
> + vq->event_triggered = false;
> +
> return vq->packed_ring ? virtqueue_enable_cb_delayed_packed(_vq) :
> virtqueue_enable_cb_delayed_split(_vq);
> }
> @@ -2044,6 +2063,10 @@ irqreturn_t vring_interrupt(int irq, void *_vq)
> if (unlikely(vq->broken))
> return IRQ_HANDLED;
>
> + /* Just a hint for performance: so it's ok that this can be racy! */
> + if (vq->event)
> + vq->event_triggered = true;
> +
> pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);
> if (vq->vq.callback)
> vq->vq.callback(&vq->vq);
> @@ -2083,6 +2106,7 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
> vq->weak_barriers = weak_barriers;
> vq->broken = false;
> vq->last_used_idx = 0;
> + vq->event_triggered = false;
> vq->num_added = 0;
> vq->use_dma_api = vring_use_dma_api(vdev);
> #ifdef DEBUG
> --
> 2.30.2
prev parent reply other threads:[~2021-07-11 4:24 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-10 23:50 [PATCH AUTOSEL 5.4 01/28] power: supply: sc27xx: Add missing MODULE_DEVICE_TABLE Sasha Levin
2021-07-10 23:50 ` [PATCH AUTOSEL 5.4 02/28] power: supply: sc2731_charger: " Sasha Levin
2021-07-10 23:50 ` [PATCH AUTOSEL 5.4 03/28] pwm: spear: Don't modify HW state in .remove callback Sasha Levin
2021-07-10 23:50 ` [PATCH AUTOSEL 5.4 04/28] power: supply: ab8500: Avoid NULL pointers Sasha Levin
2021-07-10 23:50 ` [PATCH AUTOSEL 5.4 05/28] power: supply: max17042: Do not enforce (incorrect) interrupt trigger type Sasha Levin
2021-07-10 23:50 ` [PATCH AUTOSEL 5.4 06/28] power: reset: gpio-poweroff: add missing MODULE_DEVICE_TABLE Sasha Levin
2021-07-10 23:50 ` [PATCH AUTOSEL 5.4 07/28] ARM: 9087/1: kprobes: test-thumb: fix for LLVM_IAS=1 Sasha Levin
2021-07-10 23:50 ` [PATCH AUTOSEL 5.4 08/28] PCI/P2PDMA: Avoid pci_get_slot(), which may sleep Sasha Levin
2021-07-10 23:50 ` [PATCH AUTOSEL 5.4 09/28] watchdog: Fix possible use-after-free in wdt_startup() Sasha Levin
2021-07-10 23:50 ` [PATCH AUTOSEL 5.4 10/28] watchdog: sc520_wdt: Fix possible use-after-free in wdt_turnoff() Sasha Levin
2021-07-10 23:50 ` [PATCH AUTOSEL 5.4 11/28] watchdog: Fix possible use-after-free by calling del_timer_sync() Sasha Levin
2021-07-10 23:50 ` [PATCH AUTOSEL 5.4 12/28] watchdog: imx_sc_wdt: fix pretimeout Sasha Levin
2021-07-10 23:50 ` [PATCH AUTOSEL 5.4 13/28] watchdog: iTCO_wdt: Account for rebooting on second timeout Sasha Levin
2021-07-10 23:50 ` [PATCH AUTOSEL 5.4 14/28] x86/fpu: Return proper error codes from user access functions Sasha Levin
2021-07-10 23:50 ` [PATCH AUTOSEL 5.4 15/28] PCI: tegra: Add missing MODULE_DEVICE_TABLE Sasha Levin
2021-07-10 23:50 ` [PATCH AUTOSEL 5.4 16/28] orangefs: fix orangefs df output Sasha Levin
2021-07-10 23:50 ` [PATCH AUTOSEL 5.4 17/28] ceph: remove bogus checks and WARN_ONs from ceph_set_page_dirty Sasha Levin
2021-07-10 23:50 ` [PATCH AUTOSEL 5.4 18/28] NFS: nfs_find_open_context() may only select open files Sasha Levin
2021-07-10 23:50 ` [PATCH AUTOSEL 5.4 19/28] power: supply: charger-manager: add missing MODULE_DEVICE_TABLE Sasha Levin
2021-07-10 23:50 ` [PATCH AUTOSEL 5.4 20/28] power: supply: ab8500: " Sasha Levin
2021-07-10 23:51 ` [PATCH AUTOSEL 5.4 21/28] pwm: img: Fix PM reference leak in img_pwm_enable() Sasha Levin
2021-07-10 23:51 ` [PATCH AUTOSEL 5.4 22/28] pwm: tegra: Don't modify HW state in .remove callback Sasha Levin
2021-07-10 23:51 ` [PATCH AUTOSEL 5.4 23/28] ACPI: AMBA: Fix resource name in /proc/iomem Sasha Levin
2021-07-10 23:51 ` [PATCH AUTOSEL 5.4 24/28] ACPI: video: Add quirk for the Dell Vostro 3350 Sasha Levin
2021-07-10 23:51 ` [PATCH AUTOSEL 5.4 25/28] virtio-blk: Fix memory leak among suspend/resume procedure Sasha Levin
2021-07-10 23:51 ` [PATCH AUTOSEL 5.4 26/28] virtio_net: Fix error handling in virtnet_restore() Sasha Levin
2021-07-10 23:51 ` [PATCH AUTOSEL 5.4 27/28] virtio_console: Assure used length from device is limited Sasha Levin
2021-07-10 23:51 ` [PATCH AUTOSEL 5.4 28/28] virtio: fix up virtio_disable_cb Sasha Levin
2021-07-11 4:24 ` Michael S. Tsirkin [this message]
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